Gas discharge device



Dec. 20, 1955 w. M. WEBSTER, JR 2,728,006

GAS DISCHARGE DEVICE Filed Oct. 1. 1952 2 Sheets-Sheet l INVENTOR.

WILLIm IMWEBSI ER, TR.

Dec. 20, 1955 w. M. WEBSTER, JR 2,723,006

GAS DISCHARGE DEVICE Filed Oct. 1. 1952 2 Sheets-Sheet 2 INVENTOR.

v WILLIHMM.WEBSTEB, TR.

ATTORNEY United States Patent GAS DISCHARGE DEVICE William M. Webster, Jr., Princeton, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application October 1, 1952, Serial No. 312,513

29 Claims. (Cl. 313-71) This invention relates to improvements in discharge devices containing ionizable mediums which have continuous grid control. More particularly it relates to discharge devices of a particular kind having very high values of transconductance and of anode current, and extremely low vflues of output impedance which are described in a copending application of Edward 0. Johnson, Serial No. 185,745, filed September 20, 1950, and assigned to the same assignee as the present invention.

Devices of this kind have offered very great advantages over the devices, or tubes, which preceded them. However, they also have certain limitations which will best be understood by first reviewing their basic operating principles. In any such tube there are separate discharge paths for the load current and the ionizing current. During operation, the energizing potential required for drawing the load current from a main cathode to a main anode is below the value required to produce ionization. Instead, a separate ionizing electron discharge, hereinafter called an auxiliary discharge, is energized with a higher potential to provide ionization. The auxiliary discharge ionizes the gaseous filling of the tube creating a conductive plasma by converting neutral gas atoms into positive ions and detached, free, negative electrons. The plasma surrounds the main cathode and fills the load current discharge path. As a result, the electron space charge surrounding the cathode is neutralized by positive ions and the plasma efiectively acts as low impedance conductor connected between the cathode and the anode.

The maximum load current of the device depends in a linear fashion on the plasma density (number of ionelectron pairs per unit volume produced by the auxiliary discharge) which, in turn, depends upon the current flowing in the auxiliary discharge. The actual load current may be decreased from this maximum value continuously to zero by increasing the negative potential applied to a control grid placed between the main anode and the main cathode.

Because of the fact that the load current electron discharge from the main cathode to the main anode is incapable of producing ionization, a control grid located between these electrodes is able to retain control even though it is entirely immersed in the plasma. This is a great advance over previous gas tubes in which the path of the ionizing discharge always coincided with that of the load current discharge, and therefore extended With it through the control grid openings, with the result that the grid was deprived of any further ability to control the anode current once the gaseous filling of the tube became ionized. The control grid action is such that an input signal may vary the instantaneous negative potential of the grid with the consequent result that the positive ion sheath which surrounds each grid wire will vary in thickness. The cross-sectional areas of the columns of plasma which extend through the grid openings are diminished as the ion sheaths expand. Thus, the effective impedance of the load discharge path, which 2,728,006 Patented Dec. 20, 5

depends on the plasma cross-section available to conduction, may be varied.

A further disadvantage of tubes of this type is that the load current and the auxiliary discharge paths are coplanar. This disadvantage has required highly impractical types of structures as Well as inefiicient use of the auxiliary discharge. The reason for this is that the optimum path length for the auxiliary discharge is, for most gaseous fillings, several times the mean free path of a positive ion, while the optimum path for the main discharge is approximately one ion mean free path. This restriction has required the use of unsymmetrical structures in the past in which most of the positive ions are produced several ion mean free paths from the point where they are to be used. The prior structures, if they have met the optimum path lengths, have (1) required diffusion of the plasma into the desired region; (2) have been required to produce a greater number of plasma particles in order to get the required number to difiuse into the proper region; (3) have had an active volume much greater than necessary; and (4) since the active volume and the upper frequency limit are related have been limited in maximum frequency.

One of the principal disadvantages of the tubes of this type has been that they do not utilize to best advantage the ions that are produced by the auxiliary discharge. A reason for this disadvantage is that heretofore the electrons from the auxiliary cathode have not been so directed as to uniformly surround with plasma all sides of the main cathode that are positioned in active relationship with the anode.

Still further disadvantages of tubes of this type are the cost of producing such devices and the manufacturing problems that are encountered during the manufacturing process. Some of these problems have arisen due to the duplication of parts within the tube envelope namely the two cathode heater assemblies.

A still further disadvantage of the tubes of this type that have been made heretofore is that a relatively long time must elapse while the plasma diffuses into the control electrode-anode region. This time determines the upper frequency limit of the device.

It is therefore an object of this invention to provide a novel discharge device of the type under consideration that will overcome the above mentioned disadvantages.

it is a further object of this invention to provide a new and novel means of obtaining high velocity electrons in the main cathode-control electrode region in order to efficiently provide a plasma of uniform density.

A still further object of this invention is to provide a new and novel means of obtaining high velocity electrons in the main cathode-control electrode region, as well as in the control electrode-anode region, in order to provide .a plasma of uniform density in both of these regions and thus to improve the frequency response of this device.

A still further object of this invention is to provide a new and novel structure for a discharge device of the type under consideration that is symmetrical and utilizes a composite structure.

A still further object of this invention is to provide a new and novel discharge device wherein the load current and auxiliary discharge paths are perpendicular.

A still further object of the invention is to provide a discharge device of the type under consideration that may be more easily manufactured at a reduced cost.

A still further object of this invention is to provide a composite gas discharge device of the type under consideration that will utilize the plasma formed by an auxiliary means to greatest advantage.

These and other objects and advantages have been attained by providing a composite tube comprising at least one auxiliary region adjacent a main region with an apertured element interposed between the regions. The apertures in the apertured element are concentrically arranged around the cathode so that the electron flow from the auxiliary cathode will enter the main region parallel to the axis of the main cathode at a high velocity and produce a plasma of uniform density between the main cathode and anode. The structure is arranged so that a single cathode heater assembly may be utilized for all of the cathodes. In one embodiment of this invention there is provided a plurality of auxiliary regions functioning with a main region in such a manner as to provide a plasma on both sides of the control electrode to increase the frequency response of the device.

This invention and its mode of operation-will be better understood by referring to the accompanying two sheets of drawings in connection with the following description wherein like numbers refer to like elements throughout the several views, and in which:

Figure l is a cross-sectional view of one embodiment of this invention;

Figure 2 is a transverse viewof the apertured element intermediate an auxiliary region and a main region;

Figure 3 is a cross-sectional view of another embodiment of this invention;

Figure 4 is a longitudinal section of a mount of a further modification of my invention wherein two auxiliary chambers are utilized;

Figure 5 is a longitudinal section of a modification of the discharge device shown in Figure 4; and,

Figure 6 is a circuit diagram showing one possible circuit arrangement for the operation of the tube shown in Figure 1.

Referring now to Figures 1 and 2 there is shown a discharge device comprising a sealed envelope 8 containing an ionizable medium. Any suitable ionizable medium may be utilized. The pressure with which any particular embodiment is filled will be in accordance with the electrode geometry and spacing but is not at all critical and may be varied over a wide range. A num ber of tubes of this type have been found to operate satisfactorily with a filling of helium at a pressure of approximately 750 microns. However, as is well known, other ionizable mediums and other pressures may be used.

The envelope 8 comprises a main and an auxiliary region. The main region includes a main cathode sleeve 10 which is electrically energized by the lead 11 and which is heated by the heater 14. Surrounding the main cathode 10 is a control electrode 20 which may take the form of a mesh screen or a plurality of wires supported in operative relationship with respect to the main cathode 10. A lead 27 energizes the control electrode. The spacing between the control electrode wires, or the size of the apertures in the control electrode if a mesh screen is used, should be sufliciently large to permit a plasma generated by an auxiliary discharge to readily diffuse therethrough. Surrounding the control electrode 20 is an anode 22. The anode 22 is energized by means of a lead in 25. These elements are supported by insulating member 28 and support rods upon the re-entrant stem in the usual manner as shown. The insulating member 23 may be constructed of mica.

The auxiliary region of the device comprises an auxiliary cathode sleeve 12 which, it is to be noted, utilizes the same heater wire 14 as the main cathode sleeve, and a shield 24 which surrounds the auxiliary cathode sleeve. The shield 24 is supported in operative relationship by an apertured member 16, insulating member 26 and the support rods as shown. The insulating member 26 may also be constructed of mica. The auxiliary cathode sleeve 12 is electrically energized by a lead in 13. The shield 24 may be constructed of metal or insulating material, its main purpose being to prevent a discharge from occurring between the auxiliary cathode sleeve and any other tube element except along the proper auxiliary discharge path. The auxiliary cathode sleeve 12'is supported at one end by insulating disk 18 which is in turn supported on apertured member 16 which also supports insulating disk 19 as shown. The main cathode sleeve 10 is supported at one end by insulating disk 19. This arrangement of stacked cathodes offers a very economical and practical method of using only one heater element for the two cathodes.

Between the two regions, i. e. the main and auxiliary regions, is an apertured element 16 which is supported between the insulating members 18 and 19 and is further supported by anode 22 but is insulated from the latter by insulation 30. Apertures 17 in the element 16 are of small circumference so that the electrons coming from the auxiliary region to the main region will be constricted in their passage and thus will be moving at a much greater speed when entering the main region than if the apertures were of a large cross-section. This action may be understood more fully by referring to the above identified copending application of E. 0. Johnson, Serial No. 185,745, filed September 20, 1950. Apertures 17 of approximately 50 to 60 thousandths of an inch in diameter give satisfactory operation when the tube is filled with helium to a pressure of 1 mm. Hg. However, this invention is not limited to this range in size of the apertures since the optimum aperture size depends upon the nature of the ionizable medium in the tube. The location of the apertures 17 is of considerable importance in order to most efiiciently utilize the plasma that is formed by the auxiliary discharge. If the apertures 16 are arranged in a circular pattern concentric with the cathodes, the electrons will be focused into the proper region around the sides of the main cathode and thus the plasma formed by the auxiliary discharge will be uniform in density on all sides of the main cathode 10. If the apertures 16 are arranged to open into the space existing between main cathode sleeve 10 and control electrode 20 at a distance of approximately /3 to /2 the distance from main cathode sleeve 10 to the control electrode 20, the electrons will be used most advantageously. The reason that it is desired to have the auxiliary electrons enter in this area is that the plasma that is formed will fill the main discharge nearly instantaneously and with great uniformity. This phenomenon occurs because the anode 22 is normally positive with respect to the cathode 10 and will thus have a greater attraction for the electrons than the cathode 10.

When a discharge device is made in accordance with my invention the length of the main current path is an optimum, i. e. approximately one ion mean free path, while the length of the auxiliary discharge path is also at an optimum, i.- e. several ion mean free paths. This is done without requiring an unsymmetrical structure as the paths are perpendicular. When this is done the auxiliary discharge is much more efficient.

The apertured element 16, which is shown more clearly in Figure 2, may be constructed of metal or of an insulating material. When an insulating material is used, it will be found that, adjacent the top surface of the electrode the space potential is slightly negative with respect to the auxiliary cathode sleeve while adjacent the bottom surface of the apertured electrode 16, the space potential is essentially that of the main cathode sleeve (i. e. positive with respect to the auxiliary cathode sleeve). Thus, the entire voltage drop between auxiliary cathode and main cathode appears through the apertures 17. This phenomenon permits the top surface of the apertured electrode to act effectively as a control grid while the bottom surface of the electrode will act effectively as an anode wtih respect to the auxiliary cathode 12.

If metal is used for the element 16, the electrode itself generally floats at a potential close to that of the auxiliary.

cathode. When a metal electrode is used, any desired potential may be applied to the apertured electrode, 16. When such a potential is applied to the apertured electrade 16 it will act so as to vary the degree of constriction of the auxiliary discharge electron stream by varying the effective size of the apertures. If a negative potential is applied, for example, it is found that a greater dilference of potential between the auxiliary and main cathode sleeves is required to maintain the auxiliary discharge. It is possible to modulate the main load current in this manner. When modulating the main load current with the control grid, however, I prefer to connect the apertured electrode 16 to the auxiliary cathode 12 or to permit it to float. These alternative connections are indicated by the dotted line in Figure 5.

The control electrode 20 may be made of a mesh creen which would be tubular in cross-section or it may be a plurality of wires extending from the insulating member to the insulating member 30. This control electrode 29 is adjacent the main anode 22 to allow the auxiliary discharge to ionize the gaseous filling between the main cathode 10 and the control electrode 20.

The sheath that will be formed around each member of such a negative control electrode is nothing more than a region containing positive ions enroute to the control electrode. The thickness of the sheath is determined by the positive ion current and the grid voltage. The ion current is nearly constant, being set by the rate at which ions diffuse out of the plasma. Thus, the sheath thickness will increase with negative grid voltage to such a point that adjacent sheaths overlap. Under these conditions the negative field in the sheaths will repel the electrons which would otherwise pass from the main cathode sleeve to the anode, and the anode current is then cut off. Intermediate anode current result from sheaths of intermediate radii, which in turn result from intermediate values of grid voltage.

The spacing between the control electrode 20 and the main anode 22 will vary over a considerable range and is determined by the type of operation that is desired. it has been found that the control electrode 20 may be placed so that it is almost in contact with the main anode 22. The control electrode 20 may also be moved toward the main cathode 10 a considerable distance. The controlling factor or" the spacing between the control electrode 20 and the main anode 22 is the type of operation that is desired and the voltages to be applied during this operation. For amplifier type of operation, it has been found that a spacing of 1 mm. is very satisfactory. This invention is not limited to the spacing of 1 mm. but contemplates spacings much smaller, and larger than this. An optimum spacing between the adjacent grid wires is approximately 2 mm. However, here again the invention should not be limited to this spacing but contemplates spacings both larger and smaller. A spacing between adjacent grid wires less than the mean free path of the ions will usually not permit adequate dhfusion of ions through the control electrode to furnish a plasma between it and the anode.

it should be noted that both the auxiliary cathode sleeve 1' and the main cathode sleeve 16 are heated by a common filament. This arrangement ofiers a very efiicient structure due to the fact that only one heating element need be used. The main cathode sleeve It} should contain approximately 50 percent more turns per inch than the auxiliary cathode sleeve 12. This latter structure is preferred so that the main cathode 1%) will operate at a higher temperature than the auxiliary cathode 12 and will thus be more emissive. it is desired to have the main cathode 10 more emissive in order to draw larger electron currents through the work circuit than are required in the auxiliary discharge to produce a plasma of the proper density.

in operation of this invention the auxiliary cathode sleeve 12 should be negative with respect to the main cathode sleeve 10. The control electrode 20 would normally be negative with respect to main cathode sleeve 10 but positive with respect to auxiliary cathode sleeve 12. The anode 22 is normally operated positive with respect to the main cathode sleeve 10. Thus the anode 22 will have a slightly greater attractive force for the electrons from the auxiliary region. However, due to the spacing of the apertures 17, i. e. relatively close to the cathode the attractive force exerted by the main cathode l6 and that exerted by the anode 22 will be approximately equal. Thus the plasma formed by the auxiliary discharge will be uniform throughout the main discharge region.

Although the invention has been described as having a main region comprising a main thermionic cathode 10, a control electrode 20, and an anode 22, the concepts and theory of invention are equally applicable to a main region omitting the control electrode 26 as is shown in Figure 3. This type structure may be used for such purposes as rectification wherein a control electrode is not required.

Figure 4 is a modification of the device shown in Figure 1. in this structure a plurality of auxiliary regions, one at each end of the main region, are provided and here again, one heater element 14 may be utilized to beat all of the cathodes included within the tube envelope. The main cathode 1G is supported by the insulating members l? and 1? while the control electrode 29 and the main anode 22 are supported between insulating members 30 and 3p. This structure offers the advantage that the main chamber will be thoroughly filled with plasma more quickly and the density of the plasma will be more uniform than with the structure shown in Figure l. The other members of the tube are similar to those shown in Figure 2 and it is not believed that further description is necessary. This structure is equally applicable to the device shown in Figure 3.

Figure 5 shows a further modification of the structure shown in Figure 4. in this structure apertures 17 open into the space existing between the control electrode 20 and the main cathode 19 while a second group of apertures 23 open into the space existing between the main anode 22 and the control electrode 2%. This arrangement has been found to improve the frequency response of the device. The frequency response is improved due to the fact that it is no longer necessary to wait for the plasma to diffuse from the main cathode-control electrode space into the control electrode-main anode space. Rather, plasma generation recurs simultaneously in both regions. This type of operation is more fully explained in patent number 2,588,065 which is assigned to the same assignee as the present application, and therefore further discussion is not deemed necessary.

it should be noted that the apertured elements 21 and 21 are constructed of insulating material in Figure 4 but as has been explained they may also be constructed of a conducting material and if so may have any desired voltage applied to them. When the apertured elements 21 and 2?. are constructed of insulating material the construction of the device is simplified for it is no longer necessary to insulate the apertured electrode from the main anode 22 or from any of the cathodes.

Figure 6 shows a circuit diagram for operating the type of device under consideration in Figure l as an amplifier. The cathodes are both heated by a single heater element 14. The apertured element 16, assuming a conductive element, may be connected to the auxiliary cathode 12 as shown by the dotted line or it may be dis connected and allowed to seek its own potential. Source V is made sulhciently large so that a discharge occurs between the auxiliary cathode sleeve and the main region. The source V1 may be approximately volts. This discharge generates a plasma between the main cathode 10 and the control electrode 20 which will diff-use through 7 the control electrode 20 to the main anode 22, and will thus allow large currents to flow in the main region for small values of V2. The source V2 may be or" any desired value of approximately 24 volts but it should not be greater than the ionization potential of the gaseous filling for such applications as amplification. The input signal may be applied to the control electrode as shown.

I I claim:

1. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode and anode electrode, a plate like member closing each end of said assembly, one of said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said anode, an auxiliary cathode and coaxial shield adjacent said apertured plate like member for directing an electron discharge through said apertures and uniformly between said main cathode and said anode.

2. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode and anode electrode, a plate like member closing each end of said assembly, one of said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said anode, an auxiliary cathode and coaxial shield adjacent said apertured plate like member for directing an electron discharge through said apertures and uniformly between said main cathode, said cathodes be'mg coaxial, and said auxiliary cathode and shield being closed at their ends remote from said main electrode assembly.

3. An electron discharge device having an envelope containing a gaesous atmosphere, a main electrode assembly comprising a concentric main cathode and anode electrode, a plate like member closing each end of said assembly, said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said anode, an auxiliary cathode and coaxial shield adjacent each of said apertured plate like members for directing an electron discharge through said apertures and uniformly between said main cathode and said anode. a

4. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode and anode electrode, a plate like member closing each end of said assembly, said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said anode, an auxiliary cathode and coaxial shield adjacent each of said apertured plate like members for directing an electron discharge through said apertures and uniformly between said main cathode and said anode, said cathodes being coaxial, and said auxiliary cathode and shield being closed at their ends remote from said main electrode assembly.

5. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode, control electrode and anode electrode, a plate like member closing each end of said assembly, one of said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said control electrode, an auxiliary cathode and coaxial shield adjacent said apertured plate like member for directing an electron discharge through said apertures and uniformly between said main cathode and said control electrode.

6. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising concentric main cathode, control electrode and anode electrode, a plate like member closing each end of said assembly, one of said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said control electrode, an auxiliary cathode and coaxial shield adjacent said apertured plate like member for directing an electron discharge through said apertures and uniformly between said main cathode and said control electrode, said cathodes being coaxial, and said auxiliary cathode and shield being closed at their ends remote from said main electrode assembly.

7. An electron discharge device as in claim 5 wherein all of said cathodes are heated by a single filament.

8. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode, control electrode and anode electrode, a plate like member closing each end of said assembly, said plate like members having a plurality of apertures arranged symmetrically about said cathode and between said cathode and said control electrode, an auxiliary cathode and coaxial shield adjacent each of said apertured plate like members for direct ing an electron discharge through said apertures and uniformly between said main cathode and said control electrode.

9. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode, control electrode and anode electrode, a plate like member closing each end of said assembly, said plate like members having a plurality of apertures arranged symmetrically about said cathode. and between said cathode and said control electrode, an auxiliary cathode and coaxial shield adjacent each of said apertured plate like members for directing an electron discharge through said apertures and uniformly between said main cathode and said control electrode, said cathodes being coaxial, and said auxiliary cathodes and shields being closed at their ends remote from said main electrode assembly.

10. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode, control electrode and anode electrode, a plate like member closing each end of said assembly, said plate like members having a plurality of apertures arranged symmetrically about said cathode, the apertures in one of said plate like members being arranged between said cathode and said control electrode, the apertures in the other of said plate like members being arranged between said control electrode and said anode, and an auxiliary cathode and coaxial shield adjacent each of said apertured plate like members for directing an electron discharge uniformly through said apertures.

11. An electron discharge device having an envelope containing a gaseous atmosphere, a main electrode assembly comprising a concentric main cathode, control elec- I trode and anode electrode, a plate like member closing each end of said assembly, said plate like members having a plurality of apertures arranged symmetrically about said cathode, the apertures in one of said plate like members being arranged between said cathode and said control electrode, the apertures in the other of said plate like members being arranged between said control electrode and said anode, an auxiliary cathode and coaxial shield adjacent each of said apertured plate like members for directing an electron discharge uniformly through said apertures, said cathodes being a coaxial and said auxiliary cathodes and shields being closed at their ends remote from said main electrode assembly.

12. m1 electron discharge device as in claim 10 wherein all of said cathodes are heated by a single filament.

13. A discharge device comprising a sealed envelope containing an ionizable medium, an auxiliary cathode sleeve, a hollow member concentrically surrounding said auxiliary cathode sleeve, an insulating disk arranged on one end of said auxiliary cathode sleeve and at one end of said hollow member to close the space existing therebetween, a main cathode sleeve adjacent the other end of said auxiliary cathode sleeve, a control electrode and an anode arranged in spaced relationship around said main cathode sleeve, said anode being hollow with one end arranged adjacent the other end said hollow metallic member, an apertured element interposed between said cathode sleeves and extending between said anode and said hollow member to close the space existing therebetween, the apertures of said apertured element being arranged concentrically around said cathode sleeves and being spaced closer to said cathode sleeves than to said control electrode, a second insulating disk arranged on the other end of said main cathode sleeve and closing the space existing between said main cathode sleeve and said anode, a single heater assembly for said cathodes, the number of turns of said heater assembly in said main cathode sleeve being greater than the number of turns in said auxiliary cathode sleeve.

14. A discharge device comprising an envelope containing an ionizable medium, a means for producing a plasma including an auxiliary cathode and an apertured element defining an auxiliary region, the apertures of said apertured element being arranged concentrically about said cathode, a main thermionic cathode and a control electrode and an anode defining a main region, said plasma normally extending from said apertures into said main region with a uniform density, said plasma further extending from adjacent said main cathode sleeve to adjacent said anode, and all of said cathodes being heated by a single filament.

15. A discharge device comprising an envelope containing an ionizable medium, means including an auxiliary cathode for producing an auxiliary discharge, a thermionic cathode, a control electrode surrounding said thermionic cathode, an anode surrounding said control electrode, said cathodes being coaxial, means for focusing said auxiliary discharge to enter in a uniform manner the space existing between said cathode and said control electrode on all sides of said cathode, said auxiliary discharge forming a plasma Within said envelope, and said plasma normally extending continuously from adjacent said cathode to adjacent said anode.

16. A discharge device comprising a sealed envelope containing an ionizable medium, a pair of auxiliary regions each comprising an auxiliary cathode sleeve and a shielding member, one side of each of said auxiliary regions being closed by an insulating member, the other side of each of said auxiliary regions having a difierent apertured member extending across the ends thereof, a main cathode sleeve and a control electrode and an anode defining a main region, said main region arranged adjacent said apertured members, said apertures being arranged concentrically around said cathodes, and all of said cathodes being heated by a single heating filament, said filament having a greater number of turns per inch within said main cathode than within said auxiliary cathode sleeves.

17. A discharge device comprising a sealed envelope containing an ionizable medium, means for producing a plasma including an auxiliary cathode and an apertured element and defining an auxiliary region, a pair of said auxiliary regions, a main cathode and a control electrode and an anode defining a main region, said main region being interposed between said auxiliary regions adjacent said apertured elements, said apertures being arranged concentrically around said cathodes and spaced closer to said main cathode than to said control electrode.

18. A gas discharge device comprising, a sealed envelope containing an ionizable medium, auxiliary discharge means for producing a plasma in said envelope, said means including a cathode, a group of electrodes comprising a main thermionic cathode and a main anode supported in operative spaced relationship and defining a main current path, said cathodes being coaxial, apertured means having therein a plurality of apertures concentrically spaced around said main cathode for focusing said auxiliary discharge whereby said auxiliary discharge and said main current path are perpendicular.

19. A gas discharge device comprising, a sealed enveiope having an ionizable medium therein, an auxiliary thermionic cathode, a main current path comprising a main thermionic cathode and a control electrode and an anode, said cathodes being coaxial, apertured means intermediate said auxiliary cathode and said main cathode, and said apertured means having therein a plurality of apertures concentrically spaced around said main cathode whereby a discharge from said auxiliary cathode is perpendicular to said main current path.

20. A gas discharge device comprising, a sealed envelope having an ionizable medium therein, plasma producing means including an auxiliary thermionic cathode, a main current path comprising a main thermionic cathode and a control electrode and an anode, said cathodes being coaxial, an apertured element intermediate said cathodes whereby a discharge from said auxiliary cathode is perpendicular to said main current path, and the apertures of said apertured element being concentrically spaced around said cathodes, said main path and said auxiliary cathode communicating one with the other through said apertures.

References Cited in the file of this patent UNITED STATES PATENTS 

